1. Field of the Invention
The present invention relates to a plastic trim strip of the type used on automative vehicles and to a method and apparatus for forming such trim strips.
2. Description of Related Art
Decorative trim strips are widely used to enhance the appearance of automotive vehicles. Typically, such trim strips are manufactured by a process which includes extrusion of a thermoplastic strip of a single unitary plastic material or multiple plies of different types or colors of plastic materials. Decorative plastic or metallic film may also be applied to the viewing surface of such trim strips.
As will be appreciated by those skilled in the art, the extruded plastic material, when cut to a desired length, will have the cut end exposed throughout the cross section of the strip. In the extrusion operation it is possible to obtain any one of a wide variety of surface appearances of the strip as extruded ranging from dull, to matted, to textured or to glossy, depending upon the type of extrusion die and operating conditions. This is well known in the art and does not form a part of the present invention. However, the surface appearance as extruded will usually be different from the surface appearance of an end cut through the cross section of the strip. The difference in appearance between a surface as extruded and a surface of such cut end is magnified in those instances in which a foam plastic strip is extruded as the cellular structure of the foam will be visible on such cut end while the surface as extruded may have a non-cellular or solid structure. Thus, for aesthetic purposes it is not desirable to have an end which is cut through the cross section of the extruded length of plastic exposed to view and much effort has been devoted to providing an end finish to such strips which is aesthetically pleasing in appearance. Frequently, it is desired that the strips terminate in tapered or pointed ends. However, whether such ends are tapered, pointed or some other configuration, it is desirable that no portion of the interior cross section of the strip be exposed and that only the decorative surface be exposed to view when the strip is attached to a vehicle.
Additionally, in many instances the surface appearance of the side of the extruded strip intended to face the vehicle is different from that of the surface intended for viewing. This is particularly true in those strips having multiple layers with the decorative layer intended for viewing having a different color than the base layer forming the side intended to face the vehicle. In those types of strips, it is commercially unacceptable for base layers to be visible when the strip is affixed to a vehicle.
Finished trim strips may be attached to a vehicle by any one of a number of means well-known to those skilled in the art. One such attachment means is a double-faced adhesive foam core strip, one side of which is attached to the vehicle and the other side of which contacts the surface of the trim strip facing the vehicle (i.e., the surface opposite the decorative viewing surface).
Numerous methods have been utilized in the past to provide decorative strips having aesthetically pleasing end portions; however, none of these have the combined advantages of aesthetics and cost economies which result from the present invention. For example, U.S. Pat. No. 4,489,019 and its divisional U.S. Pat. No. 4,579,755 disclose forming a longitudinal molding with non uniform sections. The process disclosed in such patents begins with an extrusion molded thermoplastic strip which is then reshaped to provide a remolded end portion. The extruded thermoplastic strip is placed into a mold, heated and partially fused by high frequency dielectric heating and then cooled in the mold so that the material is partially remolded. Preferably, the total volume of the whole material placed in the mold is equal to the volume of the cavity of the mold. The heated portions of the longitudinal strips are melted and flow along the surface of the cavity of each of the molds. Such patents also disclose reforming the strip around a separately molded clip which may be utilized to connect the part to the vehicle.
U.S. Pat. No. 3,959,538 discloses contoured end structures for trim strips formed from a length of extruded plastic material. The end structures have various configurations and are produced by removing a portion of the trim strip material as extruded between the side portions thereof to define a pair of V-shaped notches or recesses and then deforming the remaining portions of the trim strip adjacent the recess to close the recess and bring laterally opposite edges thereof into juxtapositional relationship. The juxtaposed edges are then bonded by heat sealing to complete the forming operation.
The method disclosed in U.S. Pat. No. 4,174,986 also begins with a length of extruded thermoplastic material such as polyvinylchloride (PVC) which is cut into segments of desired lengths. Under that invention an improved method for forming tapered ends is disclosed with the stated purpose of avoiding the tendency of the finished strip to delaminate from the substrate to which it is attached. Under that invention a V-shaped wedge is cut from an end of the strip thereby creating two similar triangular legs which are drawn together and adhered to create the pointed taper. The legs at the notched ends are bent upwardly approximately 45.degree. to counteract the tendency of the end to arch after the taper is formed.
The inventions disclosed in U.S. Pat. Nos. 4,617,209, 4,619,847 and 4,719,067 utilize separately molded end caps which are separately adhered or otherwise affixed to the trim strip to provide for the decorative end portion of the finished article.
With the exception of U.S. Pat. Nos. 4,489,019 and 4,579,755 the above-identified prior art involves costly operations of either cutting and adhering or of separately molding an end cap and adhering or otherwise connecting it to the extruded strip. Additionally, strips formed according to those inventions suffer from an aesthetic standpoint in that the parting line between the connected members is visible on the viewing surface of the finished part unless an additional decorative layer of film such as Mylar plastic or metallic foil is applied thereover.
Similarly, there is no indication in U.S. Pat. Nos. 4,489,019 and 4,597,755 that any effort is made to deal specifically with finishing the end portions as proposed in the present invention. Although parts produced according to the invention disclosed in U.S. Pat. Nos. 4,489,019 and 4,597,755 may not have a parting line on the viewing surface, the method utilized therein results in remelting the entire mass of the strip portion intended to be remolded so that all portions " . . . are melted and flow along the surface of the cavity of each of the molds." (See U.S. Pat. No. 4,489,019, column 4, lines 13 and 14). Such remelting and flowing of the melted surface results in the surface having an appearance different from that of the surface as extruded.